In "my collection", you have the option to sell a card to the public market, private or to kate (less)
When you are trading with someone, you must send the cards to his private market.If you want to sell a card but you don't know who wants it, sell it on the public market and someone will come and buy it (depending on the card and the price, it can take some time).
Selling your cards to kate will be fast but will give you less money.

The Urban Rivals team is made by lovers of all kind of Collectibles Cards Games and Trading Cards Games like: Magic the Gathering, Dominion, Vampire, Yu-Gi-Oh!, Pokemon, Wakfu TCG, Assassin Creed Recollection, Shadow Era, Kard Kombat and Might & Magic Duel of Champions.